blue line
 

Could anyone here explain how blue line speed is calculated. thks

For gliders and motorgliders, the blue line is at the best rate of climb speed, Vy. Some other (mostly light) aeroplanes also mark Vy in this way.

For multi-engined aeroplanes, the blue line usually indicates the best climb speed with the critical engine failed (or more precisely, the speed at which the airworthiness requirement for single engined climb performance has been met).

Does that help?

G

yes thks , was intrested in the multi engine calc.